Method of mixing and treating a hydrocarbon liquid to form a readily coalescing dispersion



`vSept. 8, 1970 F. D. wATsoN METHOD QF MIXING AND TREATING A HYDROCARBONLIQUID TO FORM A READILY COALESCING DISPERSION 2 Sheets-Sheet 1 Fled lay51. 1968 Sept. 8, 1979 F, D, WATSON 3,527,697

METHOD 0F MIXING AND TREATING A HYDROCARBON LlQUID To FORM A READILYCOALESCING DISPERSION Filed May 3l, 1968 2 Sheets-Sheet 2 Heder/o4l/l/aJof? m' www12.

ATTORNEY United States Patent O U.S. Cl. 208-267 4 Claims ABSTRACT OFTHE DISCLOSURE This specification discloses: An orifice mixer and amethod for intimately dispersing an aqueous treating liquid within ahydrocarbon liquid by their concurrent passage through a plurality ofmixing stages. Each mixing stage has a certain shear effect on thefluids being mixed, and the number of stages provides a desired level ofmixing energy. In each mixing stage, the liquids fiow through an openarea formed by a plurality of like-size openings which have onedimension residing between 0.0312 and 0.250 inch. The total open area(and the number of openings) may be defined by formulas which arecontingent upon the pressure differential, or head, which exists acrosseach mixing stage. Preferably, the open area is provided by a pluralityof like-size round openings.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the dispersing of an aqueous treating liquid within a liquidhydrocarbon. More particularly, it relates to an orifice mixer and amethod which provide mixing functions in response to the pressuredifferential created by the flow of fluids being mixed through smallopenings.

Description of the prior art A certain reaction between admixedimmiscible liquids may require a large surface of contact and a veryshort contact time. In situations With a prolonged contact time, thedesired reaction is accompanied by a multiplicity of undesired sideeffects such as polymerization, sludging, oxidation and carbonization. Aminimum contact time and maximum surface of contact is particularlyimportant in the treatment of liquid hydrocarbons with small amounts ofacids, caustic and other aqueous treating liquids. Then, the resultingmixture, or dispersion, is separated by influence of an electric field.Reference may be taken to the patent to R. B. Perkins, Ir., U.S. No.2,447,530 for a description of process situations of this tYP@ There aremany mixers available for intimately contacting immiscible liquids.Examples of these mixers are: expansion valves, square-angle bends,orifice-plate columns, bafe-plate columns, perforated buckets, variousmechanically driven paddle mixers, jet or nozzle mixers and pumps. Thepressure-loaded expansion valve has been extensively utilized.

These mixers cannot be readily controlled in both the contact timebetween the immiscible liquids and the fineness (or contact surfaces) ofthe dispersed liquid droplets.

In the acid treatment and following caustic neutralization of residualacidity in liquid hydrocarbons, maximum utilization of the treatingreagents and the complete neutralization of acid treated hydrocarbonhave been diflicult to achieve. The rate of transference, or reaction,of a substance (acid, caustic, etc.) between droplets of ICC one liquiddispersed within an immiscible liquid, all things being equal, isproportional to the surface of contact between the liquids. Inconventional mixers, the time of contact required to completetransference of the substance is therefore intimately associated withneness of the dispersion. As a result, a short time of contact isobtained only by very fine dispersions, which dispersions are diicult toresolve into their respective liquid phases.

In the present invention, droplet sizes in the dispersion are controlledby a novel orifice mixer and a method so as to be readily separated,especially Within an electric coalescer or treater. Repeated renewal ofthe surfaces of contact about these droplets produces an effective timeof contact equivalent to using droplets of much ner sizes.

Orifice mixers have been employed for mixing immiscible liquids.However, these prior-art orifice mixers imparted a certain level ofmixing energy to the liquids being mixed by controlling the orice sizesto obtain a desired pressure drop in liquids flowing through theorificeS. As a result, the orifice mixer had large openings forlarge-volume streams and small openings for smallvolume streams. Whilethe mixing energies of these devices were comparable for the same timeof contact, the surfaces of contact between the large and small openingversions were not.

SUMMARY OF THE INVENTION In accordance with this invention, an aqueoustreating liquid is dispersed Within a liquid hydrocarbon in an orificemixer. The liquids are passed concurrently in the mixer through aplurality of mixing stages which provide a certain level of mixingenergy for intimately and successively contacting the liquids. Theliquids fiow through each mixing stage under controlled shear conditionsfor dispersing the aqueous treating liquid into regulated droplet sizeswithin the hydrocarbon liquid. Each mixing stage has an open area(transverse to liquid How therethrough) which provides the shearconditions. The open area is formed by a plurality of like-size openingswhich have one dimension between 0.0312 and 0.250 inch. The open areahas specific physical relationships encompassed Within formuladefinitions in certain embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ow diagram of ahydrocarbon treating plant in which the orifice mixer and method of thepresent invention may be employed;

FIG. 2 is an enlarged elevation of the orifice mixer shown in FIG. 1;

FIG. 3 is a cross-section taken along line 3 3 of the orifice mixershown in FIG. 2; and

FIG. 4 is a cross-section taken along line 4-4 of the orifice mixershown in FIG. 2.

In these figures, like structures will be designated with identicalreferenced numerals.

DESCRIPTION OF SPECIFIC EMBODIMENTS Referring to the drawings, FIG. 1illustrates a flow diagram of a hydrocarbon treating plant in which thepresent invention may be used to great advantage. However, the presentinvention may be used in other plants, if desired. The plant providesfor acid and caustic treatment, in succession, of a liquid hydrocarbonstream at a refinery. More particularly, the feed to the plant is aliquid n-parain which is supplied through a pipe line 11. The n-parafnfeed includes relatively light hydrocarbons which have a maximum boilingpoint of less than 500 F. and a viscosity of about 1 centipoise. Then-parafin passes through a flow control valve 12 into an acid mixer 14.The valve 12 is associated with a ilow controller and is operated byback pressure to regulate the ow of the n-paraffin stream to be treated.Concentrated sulfuric acid in a small amount of about by weight isintroduced through line 13 into the n-paraffin feed upstream of the acidmixer 14. The n-parafiin and the sulfuric acid are intimately mixedwithin the acid mixer 14. The acid mixer 14 may be of conventionalconstruction, and in one plant, was a motor-driven, impeller-typeIIllXCI'.

The acid-hydrocarbon mixture iiows from the acid mixer 14 into anelectric coalescer or treater 15 where it is resolved into separatehydrocarbon and acid phases. The electric treater 15 may be of anysuitable design adapted to coalesce the dispersed acid droplets from thecontinuous hydrocarbon phase. More particularly, the electric treater 15employs one or more energized electrodes 16 which produce an electric-field for resolving dispersions. In the electric iield, the dispersedacid coalesces and settles to the bottom of the treater 15. The settledacid is removed from the treater 15 through line 17. The relativelyacid-free n-parain is removed from the treater 15 as an overhead productthrough line 18.

Although the electric treater 15 produces a substantially acid-freen-paraffin phase, an undesired residual amount of acid may yet remain init. For example, the hydrocarbon overhead product from the electrictreater 15 in one plant had a residual acidity of about 1000 parts permillion (as sulfuric acid). It is most desirable that this acidity beremoved from the n-paraiiin stream because of resulting corrosionproblems, and for other reasons.

The excess acidity in the n-paran stream may be removed by intimate andthorough contacting with a caustic solution. For example, causticsolution is passed in a small amount of about 5% by weight through apressure controlled valve 19 into the line 18 to commingle with then-paraffn overhead from the electric treater 15. The necessarycontacting of the caustic solution with the n-parafiin is obtainedwithin a caustic mixer 21. The caustic mixer 21, in one plant, was amotor-driven, impeller-type mechanical mixer. For completeneutralization of the residual acidity, the caustic mixer 21 providedprolonged intimate mixing of the caustic solution and the n-parafiinstream. Although sufficient contacting between the immiscible liquidscould eventually be obtained for neutralizing the residual acidity, thecontact time or residence in the caustic mixer 21 became commerciallyexcessive. In many instances, these mixing conditions also resulted insuch a fine dispersion of the injected caustic solution in the n-parainthat it is very difiicult to separate the mixed liquids.

In order to effect a separation of the intimately mixed liquids, theyare passed through line 22 into an electric treater 23. The electrictreater 23 is of any suitable design in which one or more energizedelectrodes 24 provide an electric field to resolve the dispersed causticsolution from the n-parafiin phase. The caustic-freed n-parafiin isremoved as an overhead from the electric treater 23 through the line 26.The coalesced caustic solution is removed through the line 27. Anautomatic control valve 28 in the line 26 maintains a suitable backpressure on the n-parafiin efiluent from the treater 23. A manualcontrol valve 28a may be used for this purpose, if desired. Then-parafl'in in the line 26 is sent to a suitable utilization such as toa product storage tank 29.

Mixing of an immiscible treating liquid into a liquid hydrocarbon may beobtained with greater facility by using an orlice mixer 31 of thepresent invention. The orifice mixer 31 having a plurality of mixingstages, is installed in parallel with the caustic mixer 21. Blockingvalves 32 and 33 isolate the caustic mixer 21 from lines 18 and 22 sothat :Ilow may be directed only through the orifice mixer 31. Blockingvalves 34 and 36 isolate the orifice mixer 31 so that fiow may bedirected only through the caustic mixer 21. Pressure gauges 37 and 38,and sample points 20, 30, 39, and 41, can be provided in lines 18, 20,and 22 so that operation of the orifice mixer 31 may be monitored. Theorifice mixer 31 is constructed to provide the desired intimate mixingof the caustic solution with the n-paraffin stream for substantiallycomplete neutralization of residual acidity. In the orifice mixer 31, avery short contact time occurs during mixing of the caustic solutionwith the n-parafiin stream so that side reactions such as sludging,oxidation, etc., are reduced to a minimum. As a result, optimum lowacidity is obtainable for the n-paratlin going to storage tank 29.

The orifice mixer 31 can be formed of any suitable construction as willbe apparent from the present description and by reference to FIGS. 2, 3and 4. In one embodiment the mixer 31 is formed of end-members 42 and 43which may be formed of pipe reducers. These members 42 and 43 carryfianges 42a and 43a which are interconnected with the lines 18 and `22,respectively. 'Ihe ange members 42b and 43b, tive orifice discs 44, andfour sealing rings 46, contain aligned openings in which studs 47 arereceived. Nuts 48 and 49 are threaded over lock washers 48a and 49a ontothe studs 47 to compress the sealing surfaces 46a of sealing rings 46into fluid-tight engagement with the orifice discs 44 and the flanges42h and 43b.

The orifice mixer 31 is usually provided with a body which has acylindrical ow passageway extending between an inlet and outletconnectable to lines 18 and 19. The orifice discs 44 are positionedtransverse to the longitudinal axis of the flow passageway, andpreferably, at equal spacings from one another. Each disc 44 contains aplurality of openings 49 which preferably are round and not aligned inadjacent discs. Substantially all of the liquids flowing through themixer 31 pass through these openings 49. The openings 49 in the mixer 31are arranged according to the present invention to have a particulardimension. Also, the openings 49 may have a total area open to liowwhich is defined by formulas to be hereinafter discussed.

The orifice discs 44 can be constructed of any suitable rigid material.They may be formed of a metal such as steel, or a plastic such aspolypropylene. The like-size openings 49 may be round, formed of narrowslots or spiral cuts, or other shapes, in the orifice discs 44.

The openings 49 have one dimension, which is measured across thenarrowest part of the openings, residing between 0.0312 and 0.250 inch.With openings 49 having these dimensions, the amount of shear applied ina mixing stage disperses immiscible aqueous treating liquid within aliquid hydrocarbon into regulated droplet-sizes which are readilyseparated or coalesced in an electric field. The dispersed dropletsmaintain their sizes upon passage through all subsequent mixing stages.As a result, the mixer 31 cannot produce the extremely fine dispersonswhich are so difiicult to separate. Thus, in the plant describedrelative to FIG. l, a very small amount of caustic solution can bereadily dispersed into regulated droplet sizes in the n-parafiin stream.The resulting dispersion is readily coalesced in the electric treater 23to produce a caustic-free hydrocarbon product.

The total open area of the openings 49 is correlated to the headdeveloped across the orifice disc 44. The orifice mixer 31 operates witha pressure drop between its inlet and outlet which is equal to the totalheads across all the orifice discs 44. More particularly, the open area,designated A, is taken in a plane normal to the liquid flow which passesthrough each orifice disc 44. 'I'he open area A is defined by theformulas:

Q=Ac\/: V=Q/A wherein:

Q=volumetric flow rate through each disc 44; A=tota1 area open to fiowthrough each dise 44; C=average orifice discharge constant for the openarea A; h=fluid head developed across each disc 44;

,gr-acceleration of gravity; and V=the velocity of uid flow through eachdisc 44.

Where the openings 49 are round, the approximate number n of suchopenings may be determined from the formula n=A/a wherein A is the totalarea open to ow through each of the orifice discs 44 and a is the areaof one opening 49.

In the mixer 31, each orifice disc 44 represents a mixing stage. Theimmiscible caustic solution is dispersed in one mixing stage into acertain range of droplet sizes within the n-parafin. Subsequent mixingstages do not change these droplet sizes. However, these mixing stagesrenew the surfaces of contact between the dispersed droplets and thehydrocarbon. The minimum number of mixing stages must provide renewal ofthe surfaces of contact sufficient to complete the utilization of theaqueous treating liquid. Additional mixing stages above such minimumnumber do not assist nor detract from the desired result.

The number of orifice discs 44 obviously is contingent upon the fluidhead developed across each of them, and upon the operating pressure dropt between the inlet and outlet of the mixer 31. Stated in anothermanner, the orifice mixer 31 has at least two mixing stages which areprovided by orifice discs 44; and additional mixing stages as requiredto produce a certain level of mixing energy for intimate contacting thedroplets of a dispersed first liquid into an immiscible second liquid bytheir concurrent passage through subsequent orifice discs 44.

The number of mixing stages or discs 44 can be determined experimentallywith the uids which are desired to be intimately contacted. Bench testsin the laboratory establish a minimum amount of the immiscible aqueoustreating liquid to be mixed with a hydrocarbon for producing a desiredresult by employing a dise and cylinder mixing device. This device isconventional and used to intermix liquids. In this device, the liquidsto be mixed are contained in a cylinder. A disc loosely fitting withinthe cylinder is carried on a stem. The stem is adapted to bereciprocated longitudinally within the cylinder. As a result, theliquids to be mixed are passed through a narrow opening between the discand cylinder. The resultant shear of fluid flowing through the openingcauses these liquids to be mixed. The opening between the disc andpiston is selected within the range of the dimensions defined for theopenings 49 in the orifice disc 44.

The disc is moved gently within the cylinder to start mixing of theimmiscible liquids. Then, the disc is moved at a linear velocity througha stroke length l and produces a liquid fiow through the clearanceopening at a velocity V. Generally, each mixing stage will operate at ahead h not less than is produced by a 3 p.s.i. differential (a minimumfor satisfactory operation) across each mixing stage. The Velocity Vproduced by the head h is determined from the formula: V=\/ghI wherein gis the acceleration of gravity constant. The disc is then moved, one ormore times, through the stroke length l at the same linear velocityuntil the desired utilization of the aqueous treating liquid isobtained. The number of strokes required on the disc to complete adesired reaction is representative of the total mixing energy to producethe desired result. Thus, each stroke of the piston is related to theoperation of each mixing stage of the mixer 31. Five strokes of the discwould represent five mixing stages in the mixer 31. If desired, the testmay be repeated for several pressure differentials across each mixingstage until the pressure differential and number of mixing stages areoptimized whereby the lowest amount of mixing energy is used to securethe desired utilization of aqueous treating liquid. Once the totalmixing energy, and the number of stages that are required to produce it,are determined for a set of immiscible liquids, the total open area A ofthe openings 49 in the disc 44 can be determined from the aforementionedformulas for a given operating pressure drop t across the mixer 31.

The orifice mixer 31 of the present invention was tested in a fieldapplication in a plant which is represented in FIG. 1. The n-paraffin inthe line 18 contained approximately 972 p.p.m. acidity as sulfuric acid.The caustic solution (aqueous sodium hydroxide) injected through thepressure valve 19 was of a strength between 1 and 4 weight percent. Thecaustic solution was introduced at a rate of approximately six gallonsper minute. The resulting hydrocarbon and caustic solution stream Waspassed through the orifice mixer 31 at about a 60 gallon per minute rateof flow. The orifice mixer 31, in this plant, was operated with an 18pound per square inch pressure drop between its inlet and outlet. Themixing energy required for substantially complete neutralization ofresidual acidity indicated that five mixing stages should be present inthe mixer 31. For convenience of manufacture, the flow passageway wasdesigned with a 4 diameter. The following information tabulation, asapplied in the formulas, for the mixer design was employed:

t=20 p.s.i. total (operating pressure differential t) Q=50 g.p.m.=0.lll6tts/sec. C=0.72 (polypropylene, 1/2 thick) h=4 p.s.i./0.434p.s.i./ft.=9.22 ft. per stage V=C\/2gh=0.72\/64.4 9.22\=l7.5 ft./sec.A=Q/V=(0.lll6 ft.3/sec.)

+(17.5 ft./sec.)=0.00637 ft? The largest size dimension, 0.250 inch,were used for openings 49. The openings 49 were round, and for 0.250inch diameter, the vnumber of holes required per stage were:

0.917 in.2 0.049 ing/hole The number of openings 49 were increased to 20in each disc 44 to insure operation of the mixer 31 Within the operatingpressure differential t.

Operation of the orifice mixer 31 of this design was compared with theconventional caustic mixer 21. The conventional caustic mixer 21intermixed a caustic solution of 1.6 weight percent at a rate of 5.7gallons per minute into the n-paraflin stream which entered the electrictreater 23. The n-parafiin overhead in line 26 had a residual acidity ofbetween l8 and 20 p.p.m. as sulfuric acid. The orifice mixer 31intermixed 1.3 weight percent of caustic solution at a rate of 5.6gallons per minute into the n-parafiin stream which entered the electrictreater 23. The n-parafiin overhead in line 26 had a residual acidity ofbetween 7.5 and l0 p.p.m. Additionally, the orifice mixer 31 intermixed1.8 weight percent of caustic at a rate of 5.6 gallons per minute withthe nparaffin stream which entered the electric treater 23. Then-parafiin overhead in line 26 had a residual acidity of between 8.3 and9.5 parts per million as sulfuric acid. The data indicated that with theorifice mixer 31, a completely neutralized n-paraffin overhead in line26 could be produced if 5.0 weight percent of caustic was introduced inan amount between l0 and l2 percent by volume into the n-parafiin streamwhich was sent to the electric treater 23.

In operation of the orifice mixer 31, the liquids being mixed are passedconcurrently through the flow passage through each orifice disc 44. Thedesired level of mixing energy for contacting these liquids to completea desired reaction is produced solely by the fluid flow through themixer 31 in response to this pressure differential t. The controlledshear exerted upon these liquids in each mixing stage disperses theaqueous treating liquid into regulated droplet sizes throughout theliquid hydrocarbon. This shear effect is obtained in each mixing stageby the open area A which is transverse to the liquid flowing :18.7 holestherethrough. This open area A, as previously defined, is provided byplurality of like-size openings having one dimension in the rangebetween 0.0312 and 0.250 inch.

The average orifice discharge constant C which is employed in theformulas for defining the total area of the openings 49 in the orificedisc 44 is also termed a coefficient of discharge of a standard orifice.The coefficient of discharge is practically a constant of 0.61 for thesharp-edged orifice providing the diameter of the orifice is largecompared to the thickness of the plate in which it is formed. Thiscoefficient of discharge is 0.98 for the rounded orifice where theorifice is concentric to the pipe. The coefcient of discharge at 0.61for the sharp-edged orifice is true only where the chamber on each sideof the orifice is not less than five times the diameter of the orifice.

It has been found that in the present invention, the average orificedischarge constant C, will reside in the range of between about 0.7 and1.0. For example, in the construction of the orifice disc 44 of 1/2thick polypropylene, the average orifice discharge constant C has avalue of about 0.72 for 1A diameter holes for the openings 49. Where theorifice disc 44 is formed of la" thick steel with 1A diameter holes foropenings 49, the average orifice discharge constant C is equal to about1.0. The numerical value for the average orifice discharge constant Ccan be determined from reference literature, or by laboratoryevaluations considering the material, its thickness and the opening sizefor the openings 49 of the orifice disc 44.

In the orifice mixer 31 of thepresent invention, the use of multistages,and multishear in successive stages, insures the intimate mixing ofimmiscible liquids, and especially aqueous treating liquids withlight-weight liquid hydrocarbon streams. The mixer 31 is adapted toprovide a dispersion of one liquid in another liquid which has uniformcharacteristics throughout its volume. As a result, the degree of mixingis at an optimum for completion of a desired reaction, and forsubsequent separation of the dispersed liquid from the continuous liquidin an electric coalescer or treater. Additionally, this intimate mixingwithin the mixer 31 occurs in the smallest amount of possible contacttime, namely that time required for the fluids to flow through the mixer31. The mixer 31 obviously has no moving parts, and the sole source ofenergy for the mixing is a function of the operating pressure dropacross the mixer 31.

From the foregoing description, it will be apparent to one skilled intheart, that various changes and alterations may be made to the orificemixer and method of operation without departing from the spirit of thepresent invention. It is intended that such changes and alterations comewithin the present description which is taken as illustrative and notlimitative of the present invention, whose scope is defined by theappended claims.

What is claimed is:

1. A method for mixing and treating a liquid hydrocarbon with an aqueoustreating liquid comprising the steps of:

(a) mixing said aqueous treating liquid and said liquid hydrocarbon andpassing the mixture through a rst of a plurality of mixing stages, eachof said stages containing a plurality of small openings having onedimension residing between 0.0312 and 0.250

inch to produce droplets forming a readily coalescing dispersion of saidaqueous treating liquid within said liquid hydrocarbon, and

(b) passing said dispersion from the first mixing stage through each ofthe remaining mixing stages until the aqueous treating liquid issubstantially completely utilized in treating the hydrocarbon.

2. The method of claim 1 in which the hydrocarbon has a maximum boilingpoint below about 500 F.

3. The method of claim 2 in which the aqueous treating liquid isselected from the group consisting of acids and Ibases which areemployed to treat liquid hydrocarbons.

4. A method for mixing an aqueous treating liquid with a hydrocarbonliquid by passing said liquids through a mixer which operates with apressure differential t between its inlet and outlet, comprising thesteps of (a) passing a mixture of said liquids through a flow passage insaid mixer, which fiow passage extends between an inlet and an outletand contains a plurality of mixing stages which provide a certain levelof mixing energy for intimately contacting said liquids by the liuid`flow through said mixer in response to the pressure differential t,

(b) providing controlled shear to the liquids flowing through each ofsaid mixing stages for dispersing the aqueous treating liquid intoregulated droplet sizes within the hydrocarbon liquid, said shear beingobtained in each of said mixing stages by an open area A transverse toliquid flow therethrough, and said open area A formed by a plurality oflike-size openings having one dimension residing Ibetween 0.0312 and0.250 inch, said open area A in each of said mixing stages being defined-by the formulas:

Q--volumetric ow rate through said mixer.

A=total opening area through which said liquids pass in said mixingstage, and such areas being taken in a plane transverse to liquid liow.

C=average orifice discharge constant for the open area A.

g=acceleration of gravity.

h=1iuid head developed across said mixing stage.

V=the velocity of fluid flow through said mixing stage.

References Cited UNITED STATES PATENTS 1,099,622 6/ 1914 Shiner 208-2671,187,797 `6/ 1916 Allan 208-267 2,073,253 3/ 1937 Pfau et al 208-2671,993,446 3/ 1935 Huff 208-298 2,751,425 6/ 1956 Rupp 208-177 FOREIGNPATENTS 613,971 2/ 1961 Canada.

DELB-ERT E. GAN'IZ, Primary Examiner G. J. CRASANAKIS, AssistantExaminer U.S. Cl. X.R. 20S-188, 270

